This invention relates to a scroll compressor wherein the volume of the compressor may be changed upon system demand, and wherein the back pressure force is also adjusted.
Scroll compressors provide efficient compression of the refrigerant and thus are becoming popular. On the other hand, scroll compressors do present many design challenges.
Essentially, scroll compressors are formed of two interfitting generally spiral wraps, with one of the wraps orbiting relative to the other. Compression chambers are formed on inner and outer surfaces of the wraps, and close during the orbiting movement of the orbiting scroll member. The compression chambers decrease in size as the orbiting scroll continues its orbital movement, and the refrigerant is compressed.
One challenge with the design of a scroll compressor is providing the ability to vary the output mass of the scroll compressor. This "modulation" of the output volume is desirable for many refrigerant compression applications. In general, proposed modulation schemes to date have concentrated on the mass changes.
However, with mass changes other aspects of the compressor need to be adjusted. In particular, scroll compressors often rely upon a back pressure force from a compressed gas delivered to a rear face of one of the scroll members. The purpose of the back pressure force is to resist a separating force generated from the entrapped fluid between the scroll members. However, with mass changes, the necessary back pressure force also changes. The prior art has not addressed this issue.